1. Field of the Invention
The present invention relates to spectacles or eyeglasses having a pair of lenses, vertically movable in unison in front of the wearer's eyes in order to facilitate a change in the focal length or lens color in the sight line of the wearer. More particularly, the invention pertains to eyeglasses which allow the wearer to manually change focal length without the necessity of obstructing his vision or moving the body or eye from the object.
2. Description of the Prior Art
Conventional spectacles which may be used for both close-in and far distance viewing include bifocal lenses having a lower portion for close-in viewing and an upper portion for far distance viewing and often require for close-in viewing an adjustment in the position of the spectacles on the nose or a raising of the head often with an attendant eye movement. Viewing close-in objects at levels above the eyes often requires hyperextension of the cervical spine which can be tiring and contribute to spinal deformation, particularly among the aged. Adjustment of glasses on the nose as an alternative to hyperextension can be painful, embarrassing and cause injury to the nose.
An alternative to the conventional spectacles having unifocal or bifocal lenses fixed in a unitary frame is the provision of spectacles having a pair of lenses, wherein each lens is aligned to an eye of the wearer and vertically movable in unison with respect to a fixed lower frame so that changes in focal length can be made without changing the sight line of each eye of the wearer. A second alternative similar to the first provides a second pair of lenses fixed in relation to the main frame. In the latter alternative, trifocal vision becomes practical if one pair of lenses are bifocal.
Roth, U.S. Pat. No. 2,842,029, shows a vertically adjustable pair of lenses attachable to a pair of spectacles at the nose bridge of the spectacles. Similarly, Masucci, U.S. Pat. Nos. 3,698,801 and 3,425,773, and Bell, U.S. Pat. No. 2,921,550 all illustrate a spectacle frame supporting a single pair of lenses that are vertically adjustable with respect to the frame. Each of these spectacles provides for adjusting the lens position with the hand at or near the nose bridge of the spectacles. Such spectacles have inter alia the obvious disadvantage that the wearer's vision is blocked when such an adjustmant is made. This can make the adjustment more difficult and interfere with activities of the wearer which require his undivided attention. For example, a surgeon requiring bifocal lenses during surgery would be distracted by having to put his hand in front of his face in order to alter the focal length of the glasses. Also, adjusting a pair of adjustable spectacles by placing the hand at the spectacle bridge is annoying to the wearer in some circumstances.